1. Field of the Invention
This invention relates to a display device such as a vacuum fluorescent display device which includes at least two sets of electrode groups which are arranged in directions intersecting each other to form a matrix in an envelope and driven to effect any desired graphic display, and more particularly to a display device which is adapted to prevent vibration of the electrode groups.
2. Description of the Prior Art
Recently, a flat panel display device such as a vacuum fluorescent display device, a liquid crystal display device, an EL panel, a PDP or the like has been developed and put to practical use for effecting any desired display of a letter, a figure, an image or the like as in a cathode ray tube. Such a display device is generally called a graphic display device and includes a matrix electrode structure which is so constructed that two kinds of electrode groups (X electrode group and Y electrode group) are arranged so as to be spaced from each other and extend in directions intersecting each other and picture cells which are provided at intersections between both electrode groups. The graphic display device is driven in such a manner that one of the electrode groups is scanned and a display signal is applied to the other electrode group in synchronism with the scanning, thereby selectively driving any desired picture cells for luminous display.
FIG. 6 schematically illustrates a basic structures of a vacuum fluorescent display device used in the conventional graphic display device described above. The fluorescent display device generally indicated by reference numeral 1 in FIG. 6 includes an anode substrate 2 made of a light-permeable insulating material such as glass or the like and a plurality of strip-like anodes 3 arranged in parallel to one another on an inner surface of the anode substrate 2. A phosphor is deposited on each of the anodes 3 which emits light due to impingement of electrons. Also, the fluorescent display device 1 includes an electron source which may be made of a plurality of cathodes 6 stretched on a cover plate 4 by means of supports 5 opposite to the anode substrate 2 and discharges electrons due to heating. Between the anodes 3 and the cathodes 6, there is provided a control electrode group 8 which may be made of a plurality or wire electrodes. The control electrode group 8 is arranged in a direction across the anodes 3 spaced at a predetermined distance from the anodes 3 by spacers 7 which is made of an insulating material. The wire electrodes for the control electrode group 8 each may be formed of a material such as 426 alloy which has a thermal expansion coefficient approximating to that of a material such as glass for the anode substrate 2 and side plates 9 so that the electrodes may be in a shape of a fine line by etching or fine punching. Thus, the anodes 3 and control electrode group 8 constitute X and Y electrode groups, and the phosphors located at virtual intersections of both electrode group which are viewed from an observation direction may form picture cells each constituting a display unit. In the fluorescent display device, thus constructed, when a scan signal is supplied to one of the electrode groups and a display signal is supplied to the other electrode group in synchronism with the scanning, any desired picture cells are selectively driven to effect any desired graphic display. These electrodes are housed in an envelope which is formed of the anode substrate 2, side plates 9 and cover plate 4, and is then evacuated to a high vacuum.
There is known a graphic display device other than that shown in FIG. 6 which includes an anode formed by depositedly applying a phosphor layer all over an inner surface of an anode substrate and X and Y control electrode groups stretchedly arranged above the anode so as to be vertically spaced from each other and extend in directions intersecting each other. In the graphic display device, when one of the X and Y control electrode groups is driven for scanning and a display signal is supplied to the other control electrode group while positive voltage is applied to the anode, the phosphor layer located at intersections of both X and Y control electrode groups are selectively driven to effect desired luminous display.
A graphic display device which includes, in addition to control electrodes for selecting picture cells, a linear electrode group which is arranged between anodes and cathodes to deflect electron beams is also known in the art.
In each of the conventional graphical display devices described above, when drive voltage is applied to one of the electrode groups stretched in the envelope to cause potential to be generated between the one electrode group and the other electrode group arranged opposite thereto at a predetermined interval, electrostatic attractive force is created between both electrode groups to which drive voltage is selectively applied for scanning. The electrostatic attractive force is periodically generated, which causes the electrode groups to vibrate. Furthermore, the electrode groups cause resonance depending on relationships between a cycle of scanning of the electrode groups (a drive frequency thereof) and a natural frequency of the electrode groups. As a result, the vibration is amount to a large magnitude.
Also, the electrode groups stretched in the envelope readily vibrate due to external force applied thereto. This is remarkable in a large-sized display device wherein long linear electrodes are stretched between supports spaced at a large distance from each other.
Brightness or luminance of each picture cell in each of the conventional display devices is significantly affected by a distance between the cathodes and the control electrodes. Accordingly, when the control electrodes vibrate due to the electrostatic attractive force and/or external force, the distance between the control electrodes is changed, which causes luminous display of the device to flicker and deteriorate quality of the display. In addition, vibration of the electrodes causes short circuit by contacting the electrodes with other electrodes and the display device or a driving circuit thereof is damaged.
In order to solve the above problems due to vibration of the electrode groups, there is proposed a fluorescent display device which is disclosed in Japanese Patent Laying-Open Publication No. 188837/1986. The fluorescent display device disclosed in the publication is so constructed that vibration control wire is incorporated in a plurality of linear grids stretched in parallel to one another in an envelope in a manner to extend in the direction across the grids to prevent vibration of the grids. However, the fluorescent display device disclosed fails to practice, because the manufacturing is highly troublesome and costly.
Another fluorescent display device developed for the purpose of eliminating the above problems is disclosed in Japanese Patent Application Laying-Open Publication No. 250943/1985. The fluorescent display device is so constructed that insulating spacers are provided between strip-like anodes arranged in a stripe-like manner and linear grids are put directly on the insulating spacers, thereby preventing vibration of the linear grids. However, such a construction of the fluorescent display device fails to fully prevent vibration of the linear grids, and sound or noise due to contact between the linear grids and the spacers is generated. Also, electrons is charged on the spacers, thus, a height of the spacers must be limited and the linear grids are liable to contact with phosphor layers of the anodes. Furthermore, the fluorescent display device has another disadvantage that the linear grids are readily damaged, because they are stretched under a high tension in order to prevent ther vibration.